The present invention relates to a semiconductor integrated circuit which has at least two independent substrates of the same polarity and specifically to area reduction and power consumption reduction techniques.
In some semiconductor integrated circuits, the substrate potential of a MOS element (MOS transistor) is controlled. This is because of such a characteristic that the threshold and saturation current property of the MOS element can be rendered variable by changing the substrate potential of the MOS element. An example which takes full advantage of the characteristic is such that the threshold and saturation current property are rendered variable at the times of operation and stoppage of the semiconductor integrated circuit. Specifically, during the operation of the semiconductor integrated circuit, the difference between the substrate potential and the source potential of the MOS element is 0 while the difference between the substrate potential and the source potential is a large difference during the stoppage, so that the threshold of the MOS element is higher during the stoppage than during the operation, whereby the subthreshold leakage current of the MOS element is reduced, which leads to reduced power consumption (see T. Kuroda et. al., “A High-Speed Low-Power 0.3 um CMOS Gate Array with Variable Threshold Voltage Scheme” IEEE Custom Integrated Circuit Conference 1996 PP. 53-56). To achieve the above-described substrate control over the MOS element, a layout method with improved area efficiency of a semiconductor integrated circuit has been proposed (see Japanese Patent No. 3212915).
In the above-described conventionally-proposed techniques, unique supply of a substrate potential results in such a problem that a pass which need not to necessarily be fast becomes fast, and as a result, a leakage current is caused. For a semiconductor integrated circuit which has a plurality of different substrate potentials, there has been no method for realizing a layout arrangement while maintaining high speed with higher resolution or maintaining low power consumption and small area.